In the operation of electronic equipment, it is necessary to shield against electromagnetic emissions. When the equipment is housed in metal cabinets, as is the case, for example, with a mainframe computer, the gaps between the panels which enclose a side of the cabinet, pose an EMI/RFI shielding problem.
In order to shield the gaps between adjacent panels or between a panel and the cabinet housing, there are presently available from different manufacturers gasket-like shields. One such manufacturer is Instrument Specialties Company, Inc., which offers two types of beryllium-copper finger contact strips sold under the trademark "Sticky Fingers" and identified in the advertising literature with U.S. Pat. No. 3,504,095. In the first-type strip, an adhesively coated section supports one end of each of the arched fingers, the other end of which is unsupported and free to move. In performing a shielding function, the gasket must be either directly compressed by the mating surfaces by a force directed perpendicularly to the gasket as with a panel pressed against the housing frame, or compressed with a wiping action by a force directed laterally to the gasket as occurs in the gap between adjacent coplanor panels when one panel is moved in a direction substantially orthogonal to its planar surface into position relative to an adjacent panel. The difficulty with the last mentioned commercial gasket is that the fingers are fragile and are designed to be wiped in only one direction--from their supported ends toward their free ends. If mounted between adjacent panels, extreme care must be exercised when removing a panel, because manual contact with the shielding fingers in a direction opposite to the wiping direction will severely damage the fingers and compromise the integrity of the shield. To preclude such damage, a flange may be provided on a panel edge within the gap area which may be grasped during panel removal, thereby protecting the gasket fingers. The flange is also necessary if a direct compression mode is used since the gasket would normally be mounted on the flange. Use of such a flange is undesirable since it restricts the movement of the panels. Thus, it may be necessary to open an adjoining panel before a panel with a flange may be opened. To open multiple panels to access a particular location in the cabinet can become time consuming for the service personnel. Moreover, the cost of the cabinet is increased since, for example, in the case of lift-off panels, it may be necessary to fabricate and stock several panel types to achieve the desired cabinet configuration.
As was mentioned hereinbefore, the manufacturer of "Sticky Fingers" offers a second type of gasket described in its advertising literature as the newest version. This second type was designed to be less susceptible to damage than the first type. As indicated in the literature, it includes a U-shaped end as part of the adhesively coated longitudinal section, which is adapted to retain the free movable end of the fingers when the enclosure doors are open, so as to protect against accidental damage to the strip's fingers. While offering some improvement relative to the first type of gasket, the second type is still adapted to be wiped in only one direction. If the gasket is grasped in a direction opposite to the wiping direction, during panel removal, the fingers tend to exit the U-shaped retainers and to be bent backward and damaged. Thus, it has been expedient to mount even the second type of gasket on panels which have a protective flange as described hereinbefore. Accordingly, the restrictions on panel removal still apply.
What is desirable is an EMI/RFI shielding gasket which may be installed on the panels of a cabinet structure without a flange and the accompanying restriction of panel movement; which may be compressively wiped in either lateral direction; which is more durable than those described herein; and which is relatively immune to damage from normal handling of the panels during service procedures. The double-action gasket assembly of the present invention fills such a need.